I haven't looked into Oneida Schuylers ( apart from the connections mentioned in Draper's Manuscript ) so I'm not sure who was the father of William or Peter Schuyler. Moses or Hendrick seem likely but I have no info for these lines.
Apart from Jacob Cornelius and Aunt Polly's testimony in the Draper Manuscript I don't have any additional evidence that Blatcup is the father of Moses Schuyler. The first name Philip in the Haldimand letter of 1780 might be a mistake, and I was also wondering about that since there's only the abstract for the microfilm. It may even be another rendition of Plattkopf ( Anglicized ) and not refer to the General, although I'd have to read the original to see in what context the name is mentioned. Blatcup probably knew the meaning of the German nickname ( "Flat Head" ) but I don't think he'd have necessarily taken offense to it so easily – Thonientaka:ion in turn means "Old Legs" ( the root -aka:ion refers to ancient inanimate objects, generally of a worn down, cobweb-gathering nature ), and names of this sort weren't entirely unknown among the Five Nations. The Henry / Hanyost naming discrepancy I can't account for though.
The Lieutenant Hanyost of the Bear Clan who was commissioned by congress ( and is listed as dead in the Losses Sustained ) is the one who is mentioned as "Han Yost Tha-oh-sa-gwat" in the Draper Manuscript, and noted there also as having been killed during the Sullivan expedition. This Hanyost is ( as far as I know ) unrelated to Hanyery and Blatcup. The latter two are listed under the same clan ( Wolf ) in the Losses Sustained though, which supports the assertion in the DM that they had the same mother. The list also cites "Hon-ye-ry's losses by Hy Trathroop, his brother's account at Oneida", which affirms that they are brothers, and Trathoop has the name "Tho-yen-ta-goyon" in the list above, which confirms that he is the same individual as Hanyery's brother Blatcup / Thonientaka:ion from the Draper Manuscript.
But, as to Blatcup being the father of Moses Schuyler, again the Draper manuscript is the only source for it. Schoolcraft's reference, which I just looked up, is interesting in that it does give "Han Yost" as the name of Moses Schuyler's father:
"[ Abraham Denny ] says, that the ( syenite ) stone on the hill, is the true Oneida stone, and not the white stone at the spring; was so pronounced by Moses Schuyler, son of Hon Yost, who knew it forty years ago; that the elevation gave a view of the whole valley, so that they could descry their enemies at a distance by the smoke of their fires; no smoke, he said, without fire."
The only way this could work in accordance with the DM is if "Han Yost Schuyler" in brackets at the end of Polly Maytop's first bulletin is Blatcup's European name, although that interpretation is questionable as you mention.
So from all this I'd take the following to be confirmed by at least two sources ( Losses Sustained and the Draper Manuscript ):
- Hanyere / Thohwen'karahkwen had a brother named Blatcup / Thonientaka:ion
The following to be stated only in the Draper Manuscript:
- Moses Schuyler was the son of Blatcup / Thonientaka:ion
And the following to be stated only in Schoolcraft:
- Moses Schuyler was the son of Han Yost
An argument could be made that Draper incorrectly presented Moses Schuyler as the son of Blatcup without his informants, Jacob Cornelius and Polly Maytop, actually having stated this. An argument could also be made that Schoolcraft incorrectly presented Moses Schuyler as the son of Han Yost without his informant, Abraham Denny, actually having stated this ( which is conceivable, since the story about Han Yost Schuyler and the executions for witchcraft is related earlier in the volume ). The scenario presented in Schoolcraft, with Moses as the son of Han Yost, is appealing because the source of the surname is immediately apparent. The scenario in the Draper Manuscript remains curious then only because it's anomalous ( i.e. why does Draper, or why do his informants, link Moses Schuyler to Blatcup several times when there should otherwise be no connection between the two ). A third source to settle all this would be handy. The link between the surname "Schuyler" and Thonientaka:ion in the Haldimand letter abstract still seems unlikely to be a coincidence to me in light of the Draper Manuscript ( where Blatcup is linked to Moses ), and it may be the source that can confirm Draper by giving Plattcoff the surname Schuyler, but I'll need to track down the original letter to see ( if I do this then it probably can't be until a while from now ). The Han Yost scenario does seem a bit more plausible to me now though in light of Schoolcraft, so I'd say go with that unless or until I can prove otherwise. In the meantime I'll keep an eye out for info relating to Moses Schuyler and will let you know if anything turns up.